Over the past few decades an increasing amount of awareness has been drawn toward water contamination problems worldwide. Although water is a renewable resource, it is difficult to obtain. For instance, in 2008 it was estimated that of the 70 percent of the Earth's surface that is water, only one percent of is viable freshwater for drinking (Thornton, Water Loss Control Manual. McGraw-Hill Professional: 2002). While developed countries obtain technological advancements with more efficient, effective methods of cleaning water, less developed countries lack the money, technical equipment and education to build and sustain the same structures and continue to struggle with contaminated water supplies (Bartram, J.; Howard, G., Drinking-water Standards for the Developing World. In The Handbook of Water and Wastewater Microbiology, Mara, D.; Horan, N., Eds. Academic Press: San Diego, Calif., 2003). In these countries the quality of health is severely hindered by contaminated wells, unforgiving storage methods and a lack of proper sanitation (Gleeson, and Gray, The Coliform Index and Waterborne Disease: Problems of Microbial Drinking Water Assessment. E & FN Spon: Boundary Row, London, 1997).
The United Nations has estimated that 1.1 billion people lack access to potable water and approximately 2.6 billion people have not been educated about, nor have developed, safe sanitation techniques (UN Human Development Report 2006; Beyond scarcity: power, poverty and the global water crisis; United Nations Development Programme: New York, N.Y., 2006; UN Human Development Report 2003; Millennium Development Goals: A compact among nations to end human poverty; United Nations Development Programme: New York, N.Y., 2003). With so many people living on the brink of illness and even death, a great deal of attention has been drawn to designing and implementing new and innovative methods of water purification, particularly in developing countries where the water crisis has hit the hardest. Gradually, the goal of bringing safe water to the world has developed into a series of goals from educating to finding a method of purification and distribution that will be both culturally accepted as well as sustainable (UN Human Development Report 2003; Millennium Development Goals: A compact among nations to end human poverty; United Nations Development Programme: New York, N.Y., 2003; UN The Millennium Development Goals Report 2007; United Nations: New York, N.Y., 2007).
Due to the common direct use of both ground water and runoff water, a lack of proper sanitation and poor water storage units, a wide variety of contaminants have access to the community water supplies. These contaminants include microorganisms, sediments, chemicals and heavy metals (EPA Bacterial Water Quality Standards for Recreational Waters; Office of Water: Washington D.C., 2003). These materials are likely to be found in the same water supply demonstrating that the method of purification that is used needs to be capable of treating a combination of contaminants.
Aside from sediment intrusion, another common problem associated with drinking water has been bacterial contamination. Even in more developed countries where purification and distribution systems are technologically advanced and water is closely monitored, cases of waterborne illnesses caused by bacteria are occasionally observed (Hrudey, and Hrudey, Published case studies of waterborne disease outbreaks—Evidence of a recurrent threat. Water Environment Research 2007, 79, 233-245). In developing countries, issues with bacterial contamination are more severe. The UN estimated in 2006 that an average of 1.8 million children die every year from diseases related to bacterial contamination which often cause severe diarrhea. Due to a lack of proper sanitation, bacteria can easily contaminate water supplies, either through supplying aquifers, water storage units, or by being exposed to ambient conditions once it has reached the house, although the water may have been previously subjected to decontamination. Water is used in the household for activities ranging from bathing to growing crops, which give bacteria that have infiltrated the water supply direct access to the families that obtain water from nearby lakes, rivers or the community well (Bitton, Wastewater Microbiology. 3 ed.; John Wiley & Sons, Inc: Hoboken, N.J., 2005).
Escherichia coli (E. coli) and Enterococci, both found in the large intestine of mammals, were introduced as indicator organisms to develop standards and indicate whether or not the water had been polluted with fecal contaminants (Bitton, Wastewater Microbiology. 3 ed.; John Wiley & Sons, Inc: Hoboken, N.J., 2005). In the United States standards for bacterial levels were set at 126 cells/100 mL for E. coli and 33 cells/100 mL for Enterococci under the Safe Drinking Water Act (SDWA) and the Clean Water Act (CWA). Methods of removing contaminants include filtration, disinfection, coagulation/flocculation and combinations of these three methodologies (Chaudhuri, and Sattar, Domestic Water Treatment for Developing Countries. In Drinking Water Microbiology, McFeters, G. A., Ed. Springer-Verlag NewYork Inc: New York City, 1990; pp 168-184). However, current technologies for removing contaminants are complex and expensive, limiting the use of these technologies in developing countries.
Coagulation and flocculation of bacterial flocs is based on the DLVO theory of colloidal suspensions. The DLVO theory, named after the developers Boris Derjaguin, Lev Landau, Evert Verwey, and Theodor Overbeek presupposes colloidal particles, such as flocs, have a core with a charge enveloped by a double layer with an opposing charge to the core. The particles act to attract one another via van der Waals forces and repulse one another via electrostatic repulsion based on the equation
                              β          ⁢                                          ⁢                      U            ⁡                          (              r              )                                      =                              Z            2                    ⁢                                                    λ                B                            ⁡                              (                                                      exp                    ⁡                                          (                                              κ                        ⁢                                                                                                  ⁢                        a                                            )                                                                            1                    +                                          κ                      ⁢                                                                                          ⁢                      a                                                                      )                                      2                    ⁢                                                    exp                ⁡                                  (                                                            -                      κ                                        ⁢                                                                                  ⁢                    r                                    )                                            r                        .                                              (                  Eq          .                                          ⁢          1                )            
Where λB is the Bjerrum length, κ−1 is the Debye-Hückel screening length and β−1 is the temperature in Kelvin. Altering the charges on the double layer, or compressing the double layer can have effects on the van der Waals and electrostatic interactions between particles, resulting in flocculation.
However, due to the high complexity and costs associated with current technologies, a simpler, more cost conscious method of removing contaminants is needed to permit individuals living in developing countries to obtain safe, potable water.